Lubricating oil composition

ABSTRACT

A lubricating oil composition comprising: (A) a base oil having a naphthene content of at least 30%, an aromatic content of not more than 2%, and a kinematic viscosity at 100 DEG  C. of 1.5 to 30 cSt; and (B) 0.01 to 5% by weight based on the total weight of the composition of a friction modifier. This composition is very useful as a lubricating oil for use in an automatic transmission or a continuously variable transmission, or as a lubricating oil for use in parts including a wet clutch or a wet brake of an agricultural tractor, etc.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lubricating oil composition and moreparticularly to a lubricating oil composition which is excellent infrictional characteristics, is decreased in changes with time of thefrictional characteristics and further is excellent in stability againstoxidation or oxidation stability, and thus which is useful as alubricating oil for use in various parts such as an automatictransmission, a continuously variable transmission, a brake of atractor, a power steering and so forth.

2. Description of Related Art

A lubricating oil to be used in parts including a wet clutch or a wetbrake of an automatic transmission, a continuously variabletransmission, a tractor and so forth is required to have such propertiesthat frictional characteristics, oxidation stability, corrosionresistance and rust resistance are good, and transmission torque islarge. An especially important requirement is that the ratio ofcoefficient of static friction to coefficient of kinematic friction as ameasure of frictional characteristics is small and further that thechange with time of the above ratio is small.

A lubricating oil having a high coefficient of static friction andresult in good transmission torque has heretofore been known. Thislubricating oil, however, has disadvantages in that frictionalcharacteristics are not sufficiently satisfactory and shift shock isundesirably big.

In recent years, with miniaturization of cars and with increasedproduction of FF (front engine, front wheel driven) cars, a tendencytoward miniaturization of an automatic transmission and so forth hasbeen increasingly developed. This miniaturization of the automatictransmission makes a driver more sensitive to the shift shock. Thus, inorder to reduce the shift shock and to make a car more comfortable todrive, it has become a technical subject to improve frictionalcharacteristics, especially at an initial stage.

In order to improve frictional characteristics, a lubricating oilcontaining a friction modifier has been proposed. This frictionmodifier-containing lubricating oil, however, is not sufficientlyimproved in frictional characteristics and further has a problem in thatthe frictional characteristics are reduced by degradation of oil due toits long term use (change with time). Moreover there is a tendency thatthe corrosion preventing ability drops.

As described above there has not yet been obtained a lubricating oilwhich possesses frictional characteristics which are good and aredecreased in the change with time, and further which has a hightransmission torque.

SUMMARY OF THE INVENTION

The present invention is intended to overcome the above problems and anobject of the present invention is to provide a lubricating oilcomposition which is decreased in shift shock, is great in transmissiontorque, and further has a sufficiently high corrosion-preventingability, and thus which is suitable for use in lubrication of anautomatic transmission and so forth.

It has been found that the object can be attained by compounding aspecified proportion of a friction modifier to a base oil havingspecified properties.

The present invention relates to a lubricating oil compositioncomprising:

(A) a base oil having a naphthene content of at least 30%, an aromaticcontent of not more than 2%, and a kinematic viscosity at 100° C. of 1.5to 30 cSt; and

(B) 0.01 to 5% by weight based on the total weight of the composition ofa friction modifier.

DESCRIPTION OF PREFERRED EMBODIMENTS

The base oil as the component (A) of the present composition is an oilhaving a naphthene content (% C_(N)) of at least 30%, preferably 32 to70%, an aromatic content (% C_(A)) of not more than 2%, preferably notmore than 1%, and a kinematic viscosity at 100° C. of 1.5 to 30 cSt,preferably 2 to 20 cSt. If the naphthene content is less than 30%,frictional characteristics are reduced. If the aromatic content is morethan 2%, oxidation stability is poor and the change with time isundesirably large. Moreover, if the kinematic viscosity at 100° C. isless than 1.5 cSt, the evaporation loss is undesirably large while onthe other hand if it is more than 30 cSt, the power loss due toviscosity resistance is undesirably too large.

It is preferred for the base oil of the component (A) to have suchcharacteristics as required for the usual lubricating oil, for example,(1) proper viscosity characteristics, (2) good stability againstoxidation, (3) good detergency and dispersancy, (4) good rust resistanceand corrosion resistance, (5) good low temperature fluidity, and soforth. Specifically, it is more preferred for the base oil to have aviscosity index of at least 75, particularly at least 80, a pour pointof not more than -10° C., particularly not more than -20° C., mostpreferably not more than -30° C., and a total acid value of 0.1 mgKOH/g.

As the base oil of the component (A), various mineral oils and syntheticoils can be used as long as they have the above specified properties.

Representative examples of the mineral oil which can be used as the baseoil of the component (A) include a purified oil which is obtained bypurifying a distillate oil by the usual method, said distillate oilhaving been obtained by atmospheric distillation of a paraffin basecrude oil or an intermediate base crude oil, or by vacuum distillationof a residual oil resulting from the atmospheric distillation, and adeep dewaxing oil which is obtained by subjecting the above purified oilto deep dewaxing treatment. In this case, the process for purificationof the distillate oil is not critical, and various methods can beemployed. Usually, the distillate oil is purified by applying suchtreatments as (a) hydrogenation, (b) dewaxing (solvent dewaxing orhydrogenation dewaxing), (c) solvent extraction, (d) alkali distillationor sulfuric acid treatment, and (e) clay filtration, alone or incombination with one another. It is also effective to apply the sametreatment repeatedly at multi-stages. For example, (1) a method in whichthe distillate oil is hydrogenated, or after hydrogenation, it isfurther subjected to alkali distillation or sulfuric acid treatment, (2)a method in which the distillate oil is hydrogenated and then issubjected to dewaxing treatment, (3) a method in which the distillateoil is subjected to solvent extraction treatment and then tohydrogenation treatment, (4) a method in which the distillate oil issubjected to two- or three-stage hydrogenation treatment, or after thetwo or three-stage hydrogenation treatment, it is further subjected toalkali distillation or sulfuric acid rinsing treatment, (5) a method inwhich after the treatment of the distillate oil by the methods (1) to(4) as described above, it is again subjected to a dewaxing treatment toobtain a deep dewaxed oil, and so forth can be employed.

In the practice of the above methods, it suffices that processingconditions be controlled so that the resulting oil has a kinematicviscosity at 100° C., a naphthene content and an aromatic content allfalling within the above-specified ranges.

A mineral oil obtained by deep dewaxing, i.e., deep dewaxed oil isparticularly preferred as the base oil of the component (A). This deepdewaxing is carried out by solvent dewaxing under severe conditions,catalytic hydrogenation dewaxing using a zeolite catalyst, and so forth.

As well as the aforementioned mineral oil, usual synthetic oils such asalkylbenzene, polybutene and poly(α-olefin), a synthetic oil containingsaturated hydrocarbons having fused rings and/or non-fused rings such as1-(1-decalyl)-1-cyclohexylethane or mixtures thereof can be used as thebase oil of the component (A).

The friction modifier as the component (B) of the present composition isadded to the base oil as the component (A) in a proportion of 0.01 to 5%by weight, preferably 0.1 to 2% by weight based on the total weight ofthe composition. If the proportion of the friction modifier is less than0.01% by weight, its addition is not effective. On the other hand, if itis more than 5% by weight, oxidation stability is undesirably reduced.

As the friction modifier which is used as the component (B) of thepresent composition, compounds commonly called an oiliness agent, afriction preventing agent, an extreme pressure agent and so forth can beused. Preferred examples of such friction modifiers include phosphoricacid esters, phosphorous acid esters, amine salts of phosphoric acidesters, amine salts of phosphorous acid esters, sorbitan fatty acidesters, pentaerythritol fatty acid esters, glycerine fatty acid esters,trimethylolpropane fatty acid esters, glycol fatty acid esters,carboxylic acids, carboxylic acid amides, carboxylic acid esters, metalsalts of carboxylic acids, fats and oils, higher alcohols, andsulfur-containing compounds. These compounds can be used alone or incombination with one another.

Of the above phosphoric acid esters and phosphorous acid esters, thoserepresented by the following general formulae (I), (II) and (III) arepreferred. ##STR1##

In the above formulae (I), (II) and (III), R¹ and R² may be the same ordifferent and are each an alkyl group having 4 to 30 carbon atoms, anaryl group, or an alkyl-substituted aryl group.

Representative examples of the phosphoric acid esters and phosphorousacid esters include butylacid phosphate, 2-ethylhexylacid phosphate,laurylacid phosphate, oleylacid phosphate, stearylacid phosphate,dibutylhydrogen phosphite, dilaurylhydrogen phosphite, dioleylhydrogenphosphite, distearylhydrogen phosphite, diphenylhydrogen phosphite andthe like.

The amine salts of phosphoric acid esters and phosphorous acid estersinclude the oleylamine salts, coconut amine salts, beef tallow aminesalts of the above phosphoric acid esters and phosphorous acid esters.

Representative examples of sorbitan fatty acid esters include sorbitanmonolaurate, sorbitan monooleate, sorbitan monostearate, sorbitansesqueoleate, sorbitan dioleate and mixtures thereof.

Representative examples of pentaerythritol fatty acid esters include themonoesters, diesters or triesters of pentaerythritol ordipentaerythritol and fatty acids such as capric acid, lauric acid,myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid andbehenic acid, and mixtures thereof.

Representative examples of glycerine fatty acid esters include oleicmonoglyceride, stearic monoglyceride, oleic diglyceride and mixturesthereof.

Representative examples of trimethylolpropane fatty acid esters includethe monoesters or diesters of trimethylpropane and fatty acids such ascapric acid, lauric acid, myristic acid, palmitic acid, stearic acid,oleic acid, linolic acid and behenic acid, and mixtures thereof.

Representative examples of glycol fatty acid esters include themonoesters of propylene glycol, trimethylene glycol, 1,4-butanediol orneopentyl glycol and fatty acids such as capric acid, lauric acid,palmitic acid, myristic acid, stearic acid, oleic acid, linolic acid andbehenic acid, and mixtures thereof.

As carboxylic acids, aliphatic carboxylic acids, divalent carboxylicacids (dibasic acids) and aromatic carboxylic acids can be used. Thealiphatic carboxylic acids have 8 to 30 carbon atoms and may besaturated or unsaturated. Representative examples of the aliphaticcarboxylic acid includes pelargonic acid, lauric acid, tridecanic acid,myristic acid, palmitic acid, stearic acid, eicosanic acid, behenicacid, triacontanoic acid, undecylenic acid, oleic acid, linolic acid,linoleic acid, erucic acid, and oils and fats fatty acids (e.g., coconutoil fatty acid, palm kernel oil fatty acid and the like). Representativeexamples of the divalent carboxylic acid include octadecylsuccinic acid,octadecenylsuccinic acid, polybutenylsuccinic acid, adipic acid, azelaicacid, sebacic acid, dodecane diacid and the like. The aromaticcarboxylic acid includes salicylic acid and the like.

As the carboxylic acid amide, various compounds can be used. Forexample, the reaction products of carboxylic acids as described aboveand amine compounds (e.g., diethylenetriamine, triethylenetetramine,tetraethylenepentamine, hexaethylenepentamine, heptaethyleneoctamine,tetrapropylenepentamine, hexabutyleneheptamine, and alkanolamines suchas monoethanolamine, diethanolamine and the like) can be used.

Carboxylic acid esters include aliphatic carboxylic acid esters anddicarboxylic acid esters (dibasic acid esters). As the aliphaticcarboxylic acid esters, the alkyl (e.g., methyl, ethyl, propyl, butyl,octyl, lauryl, and oleyl) esters of aliphatic carboxylic acids asdescribed above are usually used. The divalent carboxylic acid estersinclude the monoalkyl esters or glycol (e.g., propylene glycol) estersof divalent carboxylic acids as described above.

As the carboxylic acid metal salts, zinc laurate, zinc oleate, zincstearate, zinc salt of coconut fatty acid, aluminum stearate, magnesiumsalicylate and the like can be used.

As the fats and oils, both animal oils and vegetable oils can be used.Examples of the animal oils include lard, beef tallow, fish oil and thelike. Examples of the vegetable oils include soy bean oil, rapeseed oil,rice bran oil, palm oil, palm kernel oil, coconut oil and the like.

As the higher alcohols, octyl alcohol, lauryl alcohol, myristyl alcohol,oleyl alcohol, stearyl alcohol and the like.

As the sulfur-containing compounds, sulfurized oil, tee reaction productof phosphorous sulfide and pinene, and the like can be used.

The above compounds can be used as the component (B), friction modifier,of the composition of the present invention. Of these compounds,phosphoric acid esters, phosphorous acid esters or their amine salts,carboxylic acid amides, glycerine fatty acid esters, sorbitan fatty acidesters, carboxylic acid metal salts, dicarboxylic acid esters (dibasicacid esters) and mixtures comprising two or more thereof are preferred.

The composition of the present invention is obtained by adding afriction modifier as the component (B) to a base oil as the component(A). If desired, a viscosity index improver, an antioxidant, a detergentdispersant and so forth can be added to the composition of the presentinvention.

The type of the viscosity index improver is not critical. For example,polymethacrylate, polyisobutene, polyalkylstyrene, an ethylene-propylenecopolymer and so forth can be used. Of these, polymethacrylate having amolecular weight of not more than 100,000, preferably not more than50,000, which is excellent in shear stability and is able to preventchanges in viscosity for a long time, is particularly suitable. Theamount of the viscosity index improver added can be determinedappropriately; usually, it is 0.5 to 15% by weight, preferably 2 to 10%by weight based on the total weight of the composition.

As the antioxidant, compounds commonly used, such as phenol-basedcompounds, amine-based compounds, zinc dithiophosphate and the like canbe used. Representative examples are 2,6-di-tert-butyl-4-methylphenol,2,6-di-tert-butyl-4-ethylphenol,4,4'-methylenebis(2,6-di-tert-butylphenol), phenyl-α-naphthylamine,dialkyldiphenylamine, zinc di-2-ethylhexyldithiophosphate, zincdiamyldithiocarbamate, pinene pentasulfide and the like. The amount ofthe antioxidant added is 0.01 to 2% by weight, preferably 0.05 to 1% byweight based on the total weight of the composition.

As the detergent dispersant, an ashless detergent, a metal detergent andthe like can be used. In addition, a boron-containing ashless detergentcan be used. Specifically alkenylsuccinic acid imide, sulfonates,phenates and the like are preferred. Examples are polybutenylsuccinicacid imide, calcium sulfonate, barium sulfonate, calcium sulfinate,barium sulfinate, calcium salicynate and the like. The amount of thedetergent dispersant added is 0.1 to 10% by weight, preferably 0.5 to 5%by weight based on the total weight of the composition.

In addition, if necessary, suitable amounts of a corrosion preventingagent, a rubber swelling agent, a defoaming agent and the like can beadded to the composition of the present invention.

In the lubricating oil composition of the present invention, initialfrictional characteristics are good, that is, the ratio of coefficientof static friction to coefficient of kinematic friction is small, andthe shock due to speed change is small. Changes with time of thefrictional characteristics are small. Furthermore, the lubricating oilcomposition of the present invention is excellent in oxidation stabilityand corrosion resistance. Thus the lubricating oil composition of thepresent invention is suitable for miniaturization of a transmission andso forth.

Accordingly the lubricating oil composition of the present invention isquite useful as a lubricating oil for use in an automatic transmissionor a stepless transmission, or as a lubricating oil for use in partsincluding a wet clutch or a wet brake of an agricultural tractor and thelike.

Moreover the lubricating oil composition of the present invention havingcharacteristics as described above is useful as a lubricating oil to beused in a shock absorber, a power steering, an oil suspension andfurther in various construction machines and so forth.

The present invention is described in greater detail with reference tothe following examples.

EXAMPLES 1 to 10, and COMPARATIVE EXAMPLES 1 to 11

(1) Preparation of Lubricating Oil Composition

Base Oils A to E shown below were used as the base oil. To 89.3% byweight of each of Base Oils A to E were added 4.0% by weight ofpolymethyl methacrylate (weight average molecular weight: 42,000), 0.5%by weight of 2,6-di-tert-butyl-4-methylphenol, 5.0% by weight ofpolybutenylsuccinic acid imide, 0.1% by weight of an anti-corrosionagent, 1.0% by weight of a rubber swelling agent and 1% by weight of adefoaming agent to prepare Basic Oils A to E.

To these Basic Oils A to E were added the compounds shown in the tablein predetermined amounts to obtain lubricating oil compositions.

Basic Oil A

(1) Properties

Viscosity: 5.40 cSt (100° C.)

Viscosity Index: 105

Ring Analysis: % C_(A) 0.1, % C_(N) 38.0

Pour Point: -45° C.

(2) Method of Preparation

Obtained by subjecting a distillate from an intermediate base oil totwo-stage hydrogenation treatment and further to deep dewaxingtreatment.

Base Oil B

(1) Properties

Viscosity: 5.20 cSt (100° C.)

Viscosity Index: 105

Ring Analysis: % C_(A) 4.5, % C_(N) 27.0

(2) Method of Preparation

Obtained by subjecting a distillate from an intermediate base oil tosolvent extraction treatment and further to hydrogenation treatment.

Base Oil C

(1) Properties

Viscosity: 5.45 cSt (100° C.)

Viscosity Index: 83

Ring Analysis: % C_(A) 1.5, % C_(N) 50

(2) Method of Preparation

Mixture of 40% by weight of Base Oil A, 30% by weight of an oil obtainedby subjecting a distillate from an intermediate base oil tohydrogenation treatment, and 30% by weight of1-(1-decalyl)-1-cyclohexylethane.

Base Oil D

(1) Properties

Viscosity: 5.6 cSt (100° C.)

Viscosity Index: 120

Ring Analysis: % C_(A) 0.1 or less % C_(N) 19

(2) Method of Preparation

Mixture of 50% by weight of Base Oil A and 50% by weight ofpoly-α-olefin.

Base Oil E

(1) Properties

Viscosity: 5.1 cSt (100° C.)

Viscosity Index: 60

Ring Analysis: % C_(A) 4, % C_(N) 40

(2) Method of Preparation

Obtained by subjecting a distillate from a naphthenic oil to solventextraction treatment.

(2) Performance Test

The lubricating oil compositions prepared in (1) above, just afterpreparation thereof and after forced degradation, were subjected to thefollowing performance test. The results are shown in the table. Theforced degradation was performed at 150° C. for 24 hours according toOxidation Stability Test of Lubricating Oil for Internal CombustionEngine, JIS K 2514.

SAE (Society of Automotive Engineers) No. 2 Friction Test

Frictional characteristics were evaluated under the conditions shownbelow by the use of SAE No. 2 tester (manufactured by GreeningAssociation Inc.)

Test Conditions

Disc: Two paper discs for an automatic transmission made in Japan

Plate: Three steel plates for an automatic transmission in Japan

Number of revolutions of motor: 3,600 rpm

Piston pressure: 38 psi

Oil Temperature: 120° C.

A coefficient of kinematic friction (μ₁₂₀₀) at a number of revolutionsof 1,200 rpm under the above conditions and a coefficient of staticfriction (μ_(O)) at the time of stop were measured, and μ_(O) /μ₁₂₀₀ wascalculated.

Oxidation Stability Test

This test was performed at 150° C. for 96 hours according to OxidationStability Test of Lubricating Oil for Internal Combustion Engine, JIS K2514.

Corrosion Test

The state of corrosion of a copper plate was measured after 3 hours at100° C. according to JIS K 2513.

                                      TABLE                                       __________________________________________________________________________                                                 Comparative                                     Example                       Example                                         1  2  3  4  5  6  7  8  9  10 1  2  3                          __________________________________________________________________________    Component of the Composition                                                  (wt %)                                                                        Basic Oil A    99.0                                                                             99.5                                                                             99.5                                                                             99.9                                                                             99.0                                                                             99.0                                                                             -- 99.5                                                                             99.5                                                                             99.5                                                                             -- -- --                         Basic Oil B    -- -- -- -- -- -- -- -- -- -- 99.0                                                                             99.5                                                                             99.5                       Basic Oil C    -- -- -- -- -- -- 99.0                                                                             -- -- -- -- -- --                         Basic Oil D    -- -- -- -- -- -- -- -- -- -- -- -- --                         Basic Oil E    -- -- -- -- -- -- -- -- -- -- -- -- --                         Amine Salt of Oleyl-                                                                         1.0                                                                              -- -- -- -- -- 1.0                                                                              -- -- -- 1.0                                                                              -- --                         hydrogen Phosphite                                                            Oleyl acid Phosphate                                                                         -- 0.5                                                                              -- -- -- -- -- 0.5                                                                              -- -- -- 0.5                                                                              --                         Laurylhydrogen Phosphite                                                                     -- -- 0.5                                                                              -- -- -- -- -- -- -- -- -- 0.5                        Stearic Acid   -- -- -- 0.1                                                                              -- -- -- -- 0.5                                                                              -- -- -- --                         Oleyl Alcohol  -- -- -- -- 1.0                                                                              -- -- -- -- 0.5                                                                              -- -- --                         Sorbitan Monooleate                                                                          -- -- -- -- -- 1.0                                                                              -- -- -- -- -- -- --                         Results                                                                       SAE No. 2 Test (μ.sub. 0 /μ.sub.1200)                                   Fresh Oil      1.04                                                                             1.08                                                                             1.00                                                                             1.08                                                                             1.05                                                                             1.05                                                                             1.02                                                                             0.98                                                                             0.98                                                                             0.99                                                                             1.07                                                                             1.14                                                                             1.02                       Degradated Oil 1.04                                                                             1.08                                                                             1.00                                                                             1.10                                                                             1.07                                                                             1.06                                                                             1.04                                                                             0.98                                                                             0.98                                                                             0.99                                                                             1.10                                                                             1.22                                                                             1.07                       Oxidation Stability Test                                                      Viscosity Ratio                                                                              0.98                                                                             0.99                                                                             0.98                                                                             1.00                                                                             1.00                                                                             0.99                                                                             1.02                                                                             0.97                                                                             0.98                                                                             0.98                                                                             1.12                                                                             1.20                                                                             1.09                       Increase in Total Acid                                                                       0.13                                                                             0.23                                                                             0.15                                                                             0.31                                                                             0.24                                                                             0.10                                                                             0.51                                                                             0.12                                                                             0.14                                                                             0.15                                                                             1.33                                                                             1.97                                                                             1.42                       Value                                                                         Lacquer        no no no no no no no no no no no no no                         Corrosion Test 1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                      __________________________________________________________________________                                  Comparative Example                                                           4  5  6  7  8  9  10 11                         __________________________________________________________________________                   Component of the Composition                                                  (wt %)                                                                        Basic Oil A    -- -- -- -- -- -- -- --                                        Basic Oil B    99.9                                                                             99.0                                                                             99.0                                                                             -- -- 99.5                                                                             99.5                                                                             99.5                                      Basic Oil C    -- -- -- -- -- -- -- --                                        Basic Oil D    -- -- -- 99.0                                                                             -- -- -- --                                        Basic Oil E    -- -- -- -- 99.0                                                                             -- -- --                                        Amine Salt of Oleyl-                                                                         -- -- -- 1.0                                                                              1.0                                                                              -- -- --                                        hydrogen Phosphite                                                            Oleyl acid Phosphate                                                                         -- -- -- -- -- 0.5                                                                              -- --                                        Laurylhydrogen Phosphite                                                                     -- -- -- -- -- -- -- --                                        Stearic Acid   0.1                                                                              -- -- -- -- -- 0.5                                                                              --                                        Oleyl Alcohol  -- 1.0                                                                              -- -- -- -- -- 0.5                                       Sorbitan Monooleate                                                                          -- -- 1.0                                                                              -- -- -- -- --                                        Results                                                                       SAE No. 2 Test (μ.sub.0 /μ.sub.1200)                                    Fresh Oil      1.13                                                                             1.09                                                                             1.08                                                                              1.09                                                                            1.04                                                                             1.02                                                                             1.02                                                                             1.04                                      Degradated Oil 1.19                                                                             1.14                                                                             1.12                                                                             1.10                                                                             1.07                                                                             1.05                                                                             1.05                                                                             1.07                                      Oxidation Stability Test                                                      Viscosity Ratio                                                                              1.19                                                                             1.07                                                                             1.09                                                                             0.98                                                                             1.10                                                                             1.05                                                                             1.08                                                                             1.10                                      Increase in Total Acid                                                                       3.32                                                                             1.11                                                                             1.43                                                                             0.11                                                                             1.00                                                                             1.39                                                                             1.42                                                                             1.43                                      Value                                                                         Lacquer        no no no no no no no no                                        Corrosion Test 1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                                                                            1(1a)                      __________________________________________________________________________

What is claimed is:
 1. A lubricating oil composition comprising:(A) a base oil having a naphthene content of at least 30%, an aromatic content of not more than 2%, and a kinematic viscosity at 100° C. of 1.5 to 30 cSt; and (B) 0.01 to 5% by weight based on the total weight of the composition of a friction modifier.
 2. The composition as claimed in claim 1 wherein the friction modifier (B) is at least one compound selected from the group consisting of phosphoric acid esters, phosphorous acid esters, amine salts of phosphoric acid esters, amine salts of phosphorous acid esters, sorbitan fatty acid esters, pentaerythritol fatty acid esters, glycerine fatty acid esters, trimethylolpropane fatty acid esters, glycol fatty acid esters, carboxylic acids, carboxylic acid amides, carboxylic acid esters, metal salts of carboxylic acids, fats and oils, higher alcohols and sulfur-containing compounds.
 3. The composition as claimed in claim 1 wherein the base oil (A) is a mineral oil.
 4. The composition as claimed in claim 3 wherein the mineral oil is a deep dewaxed oil obtained by subjecting a purified oil to deep dewaxing treatment.
 5. The lubricating oil composition as claimed in claim 1, wherein said naphthene content of said base oil is 32 to 70%.
 6. The lubricating oil composition as claimed in claim 5, wherein said aromatic content of said base oil is not more than 1%.
 7. The lubricating oil composition as claimed in claim 6, wherein said kinematic viscosity of said base oil at 100° is 2 to 20 cSt.
 8. The lubricating oil composition as claimed in claim 3, wherein the mineral oil is a purified oil which is obtained by purifying a distillate oil, said distillate oil being obtained by atmospheric distillation of a paraffin base crude oil or an intermediate base crude oil, or by a vacuum distillation of a residual oil.
 9. The lubricating oil composition as claimed in claim 7, wherein the % by weight of said friction modifier is 0.1 to 2% by weight.
 10. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a phosphoric acid ester or a phosphorous acid ester of the formulae ##STR2## wherein R¹ and R² are the same or different and are an alkyl group having 4 to 30 carbon atoms, an aryl group or an alkyl-substituted aryl group.
 11. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a phosphoric acid ester or a phosphorous acid ester selected from the group consisting of butylacid phosphate, 2-ethylhexylacid phosphate, laurylacid phosphate, oleylacid phosphate, stearylacid phosphate, dibutylhydrogen phosphite, dilaurylhydrogen phosphite, dioleylhydrogen phosphite, distearylhydrogen phosphite and diphenylhydrogen phosphite.
 12. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is an amine salt of a phosphoric acid ester or a phosphorous acid ester selected from the group consisting of the an oleylamine salt, a coconut amine salt and a beef tallow amine salt of a phosphoric acid ester or a phosphorous acid ester selected from the group consisting of butylacid phosphate, 2-ethylhexylacid phosphate, laurylacid phosphate, oleylacid phosphate, stearylacid phosphate, dibutylhydrogen phosphite, dilaurylhydrogen phosphite, dioleylhydrogen phosphite, distearylhydrogen phosphite and diphenylhydrogen phosphite.
 13. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a sorbitan fatty acid selected from the group consisting of sorbitan monolaurate sorbitan monooleate, sorbitan monostearate, sorbitan sesqueoleate. sorbitan dioleate and mixtures thereof. of pentaerythritol or dipentaerythritol and a fatty acid selected from the group consisting of capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid, behenic acid, and mixtures thereof.
 14. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a glycerine fatty acid ester selected from the group consisting of oleic monoglyceride, stearic monoglyceride, oleic diglyceride and mixtures thereof.
 15. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a monoester or diester of trimethylolpropane and a fatty acid selected from the group consisting of capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid, behenic acid and mixtures thereof.
 16. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a glycol fatty acid ester comprising a monoester of a glycol selected from the group consisting of propylene glycol, trimethylene glycol, 1,4-butanediol and neopentyl glycol and a fatty acid selected from the group consisting of capric acid, lauric acid, palmitic acid, myristic acid, stearic acid, oleic acid, linolic acid, behenic acid and mixtures thereof.
 17. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a carboxylic acid selected from the group consisting of aliphatic carboxylic acids having 8 to 30 carbon atoms, divalent carboxylic acids and aromatic carboxylic acids.
 18. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is selected from the group consisting of pelargonic acid, lauric acid, tridecanic acid, myristic acid, palmitic acid, stearic acid, eicosanic acid, behenic acid, triacontanoic acid, undecylenic acid, oleic acid, linolic acid, linoleic acid, coconut oil fatty acid, palm kernel oil fatty acid, octadecylsuccinic acid, octadecenylsuccinic acid, polybutenylsuccinic acid, adipic acid, azelaic acid, sebacic acid, dodecane diacid and salicylic acid.
 19. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a carboxylic acid amide produced by the reaction product of a carboxylic acid and an amine compound selected from the group consisting of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexaethylenepentamine, heptaethyleneoctamine, tetrapropylenepentamine, hexabutyleneheptamine, monoethanolamine and diethanolamine.
 20. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a carboxylic metal salt selected from the group consisting of zinc laurate, zinc oleate, zinc stearate, zinc salt of coconut fatty acid, aluminum stearate and magnesium salicylate.
 21. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a fat or oil selected from the group consisting of lard, beef tallow, fish oil, soy bean oil, rapeseed oil, rice bran oil, palm oil, palm kernel oil and coconut oil.
 22. The lubricating oil composition as claimed in claim 9 wherein the friction modifier is a higher alcohol selected from the group consisting of octyl alcohol, lauryl alcohol, myristyl alcohol, oleyl alcohol and stearyl alcohol.
 23. The lubricating oil composition s claimed in claim 9, wherein the friction modifier is an aliphatic carboxylic acid ester or a dicarboxylic acid ester.
 24. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a sulfur-containing compound selected from the group consisting of sulfurized oil and the reaction product of phosphorous sulfide and pinene.
 25. The lubricating oil composition as claimed in claim 9, wherein said base oil has a naphthene content of 38%, an aromatic content of 0.1% and a kinematic viscosity of 5.4 cSt at 100° C.
 26. The lubricating oil composition a claimed in claim 25, wherein said base oil is contained in an amount of 99 wt. % and said friction modifier is an amine salt of oleyl hydrogen phosphite contained in an amount of 1 wt. %.
 27. The lubricating oil composition a claimed in claim 25, wherein said base oil is contained in an amount of 99.5 wt. % and said friction modifier is oleyl acid phosphate contained in an amount of 0.5 wt. %.
 28. The lubricating oil composition as claimed in claim 25, wherein said base oil is contained in an amount of 99.5 wt. % and said friction modifier is lauryl hydrogen phosphite contained in an amount of 0.5 wt. %.
 29. The lubricating oil composition s claimed in claim 25, wherein said base oil is contained in an amount of 99.9 wt. % and said friction modifier is stearic acid contained in an amount of 0.1 wt. %.
 30. The lubricating oil composition as claimed in claim 25, wherein said base oil is contained in an amount of 99 wt. % and said friction modifier is oleyl alcohol contained in an amount of 0.1 wt. %.
 31. The lubricating oil composition as claimed in claim 25, wherein said base oil is contained in an amount of 99 wt. % and said friction modifier is sorbitan monooleate contained in an amount of 0.1 wt. %.
 32. The lubricating oil composition as claimed in claim 9, wherein the friction modifier is a pentaerythritol fatty acid ester selected from the group consisting of a monoester, a diester and a triester of pentaerythritol or dipentaerythritol and a fatty acid selected from the group consisting of capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid, behenic acid, and mixtures thereof. 